1. Field of the Invention
The present invention relates to a motor and more particularly to a structure for mounting a stator core having a plurality of salient poles to a motor frame.
2. Description of the Related Art
FIG. 6 shows a structure of a prior art motor, i.e. a structure of a motor having a stator core on which a plurality of salient poles are formed as a stator part of the motor. In more detail, the figure shows a magnetic disk driving unit comprising a hub for mounting a magnetic disk (not shown) and the motor having the stator core for rotating and driving the magnetic disk in the hub. In the figure, the cup shaped hub 32 is secured to a rotating shaft 31. The magnetic disk is mounted on the peripheral part of the hub 32 to rotate and drive in one body with the rotating shaft 31. A driving magnet 34 is attached within the inner peripheral part of the hub 32. The rotating shaft 31, hub 32 and driving magnet 34 compose a rotor section of the motor.
Disposed at a position facing the driving magnet 34 is the stator core 35 and a coil 38 is wound around each salient pole of the stator core 35 a predetermined number of times. The neighborhood of a base side 36 of the plurality of salient poles of the stator core 35 is mounted on a cylindrical support (outer peripheral part) 40 attached to a motor frame 39. That is, the neighborhood of the base side 36 of the plurality of salient poles is mounted on the support 40 and it secured thereto by an adhesive or the like. The stator part of the motor comprises the stator core 35 on which the salient poles are formed, the coil 38 wound around each of the salient poles and the motor frame 39.
On the other hand, a pair of ball bearings 41 disposed by being separated by a predetermined distance in the axial direction are secured between the rotating shaft 31 and the inner peripheral part of the support 40.
Although the stator core 35 shown in FIG. 6 is constructed so that it has a thickness in the axial direction of the rotating shaft 31 because it is wound by the coil 38 in the longitudinal direction thereof which is parallel to the axial direction, it is caused by a convenience in using recording media mounted.
The driving magnet 34 and the stator core 35 on which the salient poles are wound by the coil 38 compose a magnetic circuit.
In the structure of the prior art motor described above, however, only the neighborhood of the base side 36 of each salient pole of the stator core 35 is mounted and an edge side 37 of each salient pole of the stator core 35 is in free end state, i.e. it floats against the motor frame 39, so that a magnetic imbalance is caused due to a magnetic distribution and the like of the driving magnet 34 during driving of the motor. The magnetic imbalance causes the stator core 35 to vibrate, generating a vibration of the motor itself as a result.
Especially for the type of magnetic disk driving unit shown in FIG. 6, strict conditions are imposed on the stabilization of rotation and drive of the motor in order to increase the capacity of the magnetic disk by narrowing down the width of recording track to improve recording density thereon and to downsize the motor itself.
Further, there has been a disadvantage in the prior art motor structure that when the motor is flattened, its shock resistance becomes weak because enough wall thickness cannot be taken for the motor frame 39. If the shock resistance is weak, it causes a problem that when equipment on which such magnetic disk driving unit as described here is mounted, i.e. a computer, is dropped by mistake, the motor frame 39 will be broken, thereby disabling the computer.
U.S. Pat. Nos. 4,965,476 and 5,157,295 show the use of a stabilizer ring for stiffening purposes and to modify the frequency of vibration of a motor.